This invention relates to a semiconductor device having a barrier metal layer for suppressing diffusion of any of the elements constituting the interconnects of the device. It also relates to a method of manufacturing such a device.
Generally, a semiconductor device has a barrier metal layer arranged at the bottom or the side sides of the metal interconnects of the device. Such a barrier metal layer prevents mutual diffusion and reaction of the interconnection metal and the silicon diffusion layer, diffusion of the interconnection metal into the interlayer dielectric film surrounding the interconnection layer and reaction of the metals of the via-plug and the interconnection layer if they are made of different metals.
Barrier metal is required to show a sufficient extent of barrier effect of suppressing diffusion and reaction of the metal of the interconnection layer of semiconductor devices in the process of manufacturing the devices and during the operation of the devices due to the electric field and the high temperature existing in the devices. At the same time, it is required to be very thin in such a manner that it may not raise the effective electric resistance of the interconnects. Then, barrier metal showing a low resistivity and a low electric contact resistance has to be used in order not to raise the electric resistance at the contacts and the via-plug. Additionally, it is required to adhere well to the interlayer dielectric film and the interconnection layer.
Monolayer barrier metal of metal nitride such as TiN or TaN is known to show a satisfactory level of barrier effect in known semiconductor devices and have characteristic properties required thereto. However, with the current trend for a higher degree of integration and the use of miniature elements, a very thin barrier metal layer comes to be used in semiconductor devices at the cost of a satisfactory barrier effect.
Additionally, as copper is used popularly for the interconnection layer of semiconductor devices in recent years in an attempt for realizing high speed operation and high reliability, any known barrier metal can no longer provide a sufficient level of barrier effect of preventing copper from rapidly diffusing into the silicon substrate and the dielectric layer. Still additionally, the resistivity and the electric contact resistance of the barrier metal of a semiconductor device are required to become lower in order to make the device operate at higher speed. In short, known barrier metal can no longer provide a sufficient level of barrier effect and electric characteristics.
The insufficient barrier effect of known barrier metal is particularly remarkable in non-aluminum type metal interconnects. This is because the thin aluminum oxide film covering aluminum interconnects operates effectively as a tight barrier film. Such an aluminum oxide film layer is formed as a native oxide particularly along the interface of a metal other than aluminum and an aluminum alloy and conduction of electricity across the interface can take place in the form of tunnelling current because of the small film thickness. On the other hand, while copper, silver, gold and alloys of any of them can be used for interconnection as they show a resistivity lower than that of aluminum, they cannot be expected to form a good oxide layer as in the case of aluminum. Thus, there is a strong demand for a novel barrier metal film that provides a barrier effect better than ever.
Therefore, it is the object of the present invention to provide a semiconductor device having a barrier metal layer that shows a high barrier effect and good electric characteristics relative to the metal of the interconnection layer of the device and also a method of manufacturing such a semiconductor device.
According to a first aspect of the invention, the above object is achieved by providing a semiconductor device comprising:
a base layer;
a barrier metal layer formed on the base layer; and
a metal interconnect formed on the barrier metal layer;
the barrier metal layer being made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from a group of boron, oxygen, carbon and nitrogen and having a laminated structure formed of at least two compound films xcex1xcex2n with different compositional ratios in atomic level, n being a ratio of the number of atoms of the element xcex2 relative to the number of atoms of the element xcex1.
For the purpose of the invention, the barrier metal may have a structure that shows a continuous compositional change.
Preferably, the metal element belongs to one of a IVB group, a VB group and a VIB group.
Preferably, at least one of the at least two compound films xcex1xcex2n is a compound film xcex1xcex2x (x greater than 1) made of the element xcex1 and the element xcex2.
Preferably, the compound film xcex1xcex2x (x greater than 1) has a film thickness not greater than 10 nm.
According to a second aspect of the invention, there is provided a semiconductor device comprising:
a base layer;
a barrier metal layer formed on the base layer; and
a metal interconnect formed on the barrier metal layer;
the barrier metal layer being made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from a group of boron, oxygen, carbon and nitrogen and having a laminated structure formed of at least two compound films xcex1xcex2n with different compositional ratios in atomic level, n being a ratio of the number of atoms of the element xcex2 relative to the number of atoms of the element a
the elements xcex1 contained in the at least two compound films xcex1xcex2n being same and identical;
at least one of the at least two different compound films xcex1xcex2n being a compound film xcex1xcex2x (x greater than 1) made of the element xcex1 and the element xcex2.
For the purpose of the invention, the barrier metal may have a structure that shows a continuous compositional change.
Preferably, the barrier metal layer is formed by laying the compound film xcex1xcex2x (x greater than 1) on a compound film xcex1xcex2y (yxe2x89xa61) made of the element xcex1 and the element xcex2 and the metal interconnect is in contact with the compound film xcex1xcex2x (x greater than 1).
Alternatively, the barrier metal layer may be formed by laying a compound film xcex1xcex2y (yxe2x89xa61) made of the element xcex1 and the element xcex2 on the compound film xcex1xcex2x (x greater than 1); and
the metal interconnect may be held in contact with the compound film xcex1xcex2y (yxe2x89xa61).
Still alternatively, the barrier metal layer may be formed by laying sequentially a compound film xcex1xcex2y (yxe2x89xa61) made of the element xcex1 and the element xcex2, the compound film xcex1xcex2x (x greater than 1) and another compound film xcex1xcex2y (yxe2x89xa61) to form a laminate.
Preferably, the x is not smaller than 1.2 and the y is not greater than 0.9.
Preferably, a total film thickness t of the compound film xcex1xcex2x (x greater than 1) and a total film thickness T of the barrier metal show a relationship of t/Txe2x89xa60.3.
Preferably, the metal element belongs to one of a IVB group, a VB group and a VIB group.
Preferably, a film thickness of the compound film xcex1xcex2x (x greater than 1) is not greater than 10 nm.
According to a third aspect of the invention, there is provided a semiconductor device comprising:
a base layer;
a barrier metal layer formed on the base layer; and
a metal interconnect formed on the barrier metal layer;
the barrier metal layer having a compound film xcex1xcex3x made of at least one element a selected from metal elements and at least one element xcex3 selected from boron, carbon and nitrogen and a compound film xcex1xcex3yOz made of the element xcex1, the element y and oxygen (O) arranged to form a laminate, each of x and y being a ratio of the number of atoms of the element y relative to the number of atoms of the element xcex1xcex3x and Z being a ratio of the number of atoms of the oxygen relative to the number of atoms of the element a.
Preferably, x is not smaller than 0.2.
Preferably, a film thickness of the compound film xcex1xcex3yOz is not greater than 3 nm.
Preferably, the metal element belongs to one of a IVB group, a VB group and a VIB group.
A manufacturing method of the above device preferably comprises the steps of:
forming the compound film xcex1xcex3x on the base layer;
forming the compound film xcex1xcex3yOz by oxidizing a surface of the compound film xcex1xcex3x; and
forming the metal interconnect on the compound film xcex1xcex3yOz.
According to a fourth aspect of the invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
forming a compound film xcex1xcex3x made of at least one element a selected from metal elements and at least one element y selected from boron, carbon and nitrogen on a base layer containing oxygen (O); and
forming a compound film xcex1xcex3yOz by causing the compound film xcex1xcex3x to reduce the base layer and thereby oxidizing the compound film xcex1xcex3x on an interface of the compound film xcex1xcex3x and the base layer.
Preferably, the base layer is a dielectric film layer or a metal interconnection layer.
For the purpose of the invention, a metal inter-connect includes a metal electrode such as a plug electrode.
Now, the background, the effects and the advantages of the invention will be discussed below.
Conventionally, sputtering and CVD are used as popular techniques for forming a metal compound film as barrier metal layer relative to the metal of an inter-connection layer. The most popular technique is the reactive sputtering method of causing Ar gas and gas containing an additive element to flow simultaneously, using a metal target, to form a film. With the reactive sputtering method, metal nitride films may be formed with various different compositions by modifying the flow rate of Ar gas and that of N2 gas in various different ways. However, as the ratio of the number of nitrogen atoms relative to the number of atoms of the metal element (an atomic ratio of nitrogen/metal) approaches 1, the nitrogen content of the film would not increase simply by raising the flow rate of N2 gas and, therefore, it has been difficult to produce a metal nitride film whose ratio of the number of nitrogen atoms relative to the number of atoms of the metal element exceeds 1.
Under these circumstances, the inventors of the present invention found that a TaN film whose ratio of the number of nitrogen atoms relative to that of Ta atoms exceeds 1 can be formed by supplying Ar gas and N2 gas simultaneously into a chamber, using a Ta target, and heating the substrate temperature to about 300xc2x0 C. under a condition adapted to form a TaNx film.
When the barrier effect of the obtained TaNx film relative to Cu, it was found that the barrier effect was remarkably improved when the ratio of the number of nitrogen atoms relative to that of Ta atoms exceeded 1 and still further when the ratio exceeded 1.2, as shown in FIG. 1.
This improvement of the barrier effect may be realized because the number of rapid diffusion paths such as crystal grain boundaries is reduced as the film is progressively turned amorphous by excessive nitrogen contained in the TaN film. As a result of an observation using X-ray diffractometry, the obtained TaN film was found substantially amorphous because no clear diffraction peaks of TaN were recognized when the N/Ta ratio exceeded 1.2.
However, such a TaNx (x greater than 1) film is accompanied by a problem of a large resistivity and hence it cannot be used as barrier metal for Cu interconnects. Therefore, the inventors of the present invention continued the research effort to find that a barrier metal having a small resistivity and a high barrier effect can be obtained by laying a plurality of layers of compound film xcex1xcex2n made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from boron, oxygen, carbon and nitrogen to form a laminate.
Particularly, a barrier metal according to the invention can be made to reduce its via resistance and interconnect resistance without sacrificing its high barrier effect when a compound film xcex1xcex2x (x greater than 1) made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from boron, oxygen, carbon and nitrogen and a compound film xcex1xcex2y (yxe2x89xa61) made of the elements xcex1 and xcex2 are combined. Further, a laminated film can be made by changing the mixing ratio of xcex2 in the barrier metal formation process. It provides a easy process to form a laminated film in a short process time.
Additionally, a barrier metal according to the invention can be made to show a low via resistance, a low interconnect resistance and a high barrier effect when it is realized by laying a compound film xcex1xcex2y (yxe2x89xa71) made of the elements xcex1 and xcex2, a compound film xcex1xcex2x (x greater than 1) also made of the elements xcex1 and xcex2 and another compound film xcex1xcex2y (yxe2x89xa61) to form a laminate.
As a result of another research apart from the one described above, the inventors of the present invention also found that a barrier metal showing a low resistance and a high barrier effect can be obtained by laying a compound film xcex1xcex3x made of at least one element xcex1 selected from metal elements and at least one element xcex3 selected from boron, carbon and nitrogen and a compound film xcex1xcex3yOz made of the elements xcex1 and y and oxygen (O) to form a laminate.
A compound film xcex1xcex3yOz can be produced by oxidizing the exposed surface of a compound film xcex1xcex3x. Alternatively, a compound film xcex1xcex3yOz can be produced by forming a compound film xcex1xcex3x on a base member typically made of SiO2 and hence containing oxygen or on metal interconnects, subsequently reducing the base member or the metal interconnects by means of the compound film xcex1xcex3x and thereby oxidizing the compound film xcex1xcex3x.
As described above, according to the invention, a barrier metal showing a low resistance and a high barrier effect by laying a plurality of compound films xcex1xcex2n, each being made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from boron, oxygen, carbon and nitrogen.
Particularly, a barrier metal according to the invention can be made to reduce its via resistance and interconnect resistance without sacrificing its high barrier effect when it is formed by combining a compound film xcex1xcex2x (x greater than 1) made of at least one element xcex1 selected from metal elements and at least one element xcex2 selected from boron, oxygen, carbon and nitrogen and xcex1 compound film xcex1xcex2x (xxe2x89xa61) also made of the elements xcex1 and xcex2. Such a barrier metal can be produced with a short process time because a film laminate can be prepared by modifying the mixture ratio of xcex1 and xcex2.
According to the invention, a barrier metal showing a low resistance and a high barrier effect can also be formed by laying a compound film xcex1xcex3x made of at least one element xcex1 selected from metal elements and at least one element xcex3 selected from boron, carbon and nitrogen and a compound film xcex1xcex3yOz made of the elements xcex1 and xcex3 and oxygen (O).
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.